# Which is nonpolar: CF_4 or CH_2F_2?

$C {F}_{4}$ is non-polar.
Molecular polarity results from the vector sum of the individual ${C}^{\delta +} \rightarrow {F}^{\delta -}$ dipoles. Given a tetrahedron (and $C {F}_{4}$ certainly assumes this structure), the $C - F$ dipoles sum to $0$ (remember that the vector sum is the geometric sum). The $C - H$ bond is fairly non-polar, and thus their equivalent vector sum with $C - F$ dipoles is non-zero.
The same situation obtains when non-polar $C {\left(C l\right)}_{4}$ is compared to polar chloroform, or (more polar) methylene chloride.